The original Chords Trainer (1982)

The description on the package says (note: typos are in original text):

The Chords Trainer is fundamentally the unifying concept of theoretical and harmonical information of music and may become especially for beginners an essential device to work with.
Tecnically the Chords Trainer presents itself as an instrument of easy consultance for everybody: a real and outstanding system of simultaneous information.
Who will carefully consult the Chords Trainer, will put himself in a condition to apply, with an own harmonical instrument, not only the chords, but also the relative harmonical successions.